Compound (1), 4-[5-(pyridin-4-yl)-1H-1,2,4-triazol-3-yl]pyridine-2-carbonitrile, is known to serve as a drug which has a xanthine oxidase inhibitory action and which can lower serum uric acid level (Patent Document 1).

There have been reported several methods for producing the above compound (1). In one production method, methyl isonicotinate N-oxide is subjected to Reissert Henze reaction, to thereby form methyl 2-cyanoisonicotinate, which is transformed into a hydrazide, and the hydrazide is condensed with 4-cyanopyridine (Patent Document 1, Example 12). In another production method, isonicotinic acid N-oxide is transformed into a hydrazide, into which a cyano group is incorporated through Reissert Henze reaction, and the product is condensed with 4-cyanopyridine (Patent Document 1, Example 39). In an alternative production method, 4-cyanopyridine-N-oxide (starting material) is condensed with isonicotinic acid hydrazide, to thereby form a triazole ring, which is then protected (Patent Document 2) or non-protected (Patent Document 3), and a cyano group is incorporated into the product through Reissert Henze reaction, to thereby yield compound (1).
Meanwhile, crystalline polymorphism means such a condition that a compound formed of a unique molecule having a unique chemical composition exists in two or more crystal forms having different molecular arrangements. When a pharmaceutical compound is such a compound, pharmacological activity, solubility, bioavailability, stability, and the like of the compound are known to vary depending on the physicochemical properties intrinsic to the polymorph. Thus, when the useful pharmaceutical compound includes crystalline polymorphs, a compound of a crystal form which provides high utility is preferably produced.